Sparkplug cap

ABSTRACT

A sparkplug cap with a plastic insulating body containing the ignition cable terminal and the sparkplug terminal and a grounded screening jacket surrounding the same. The ignition cable terminal and/or sparkplug terminal are in the form of a condenser electrode which is enclosed in the plastic insulating body. Utilizing the plastic insulating body as dielectric, they form with the screening jacket a capacitor of high capacitance connected in parallel to the spark gap. The screening jacket forms a metallic sleeve, coil spring or metallic fabric. The inner condenser electrode is formed as a hollow cartridge and contains screened therewithin a radio interference-suppression resistor. The capacitor is connected behind the noise-suppression resistor, in the direction of the ignition current.

[ Aug.8,1972

United States Patent Baur [54] SPARKPLUG CAP [72] Inventor:

FOREIGN PATENTS OR APPLICATIONS Heini Baur, Hardegsen, Germany 1935 Great Britain...............315/53 [73] Assignee: Firma Baur Elektronik GmbH, Har- Primary Examiner-Alfred L. Brody Attorney-Ernest G. Montague degsen, Germany Feb. 3, 1970 Appl. No.: 8,174

[22] Filed:

[57] ABSTRACT A sparkplug cap with a plastic insulating body containing the ignition cable terminal and the sparkplug terminal and a grounded screening jacket surrounding the same. The ignition cable terminal and/or sparkplug terminal are in the form of a condenser electrode which is enclosed in the plastic insulating body. Utilizing the plastic insulating body as dielectric, they form with the screening jacket a capacitor of high [56] References Cited capacitance connected in parallel to the spark gap. The screening jacket forms a metallic sleeve, coil UNITED STATES PATENTS spring or metallic fabric. The inner condenser elec- 2 173 766 .9/1939 X trode is formed as a hollow cartridge and contains 2,640,174 5/1953 screened therewithin a radio interference-suppression 3,191,133

Short et al. ..............3l5/59 X resistor. The capacitor is connected behind the noisesuppression resistor, in the direction of the ignition 6/1965 Texsier... ...3l5/58 X 11 Claims, 3Drawing Figures wf lllllllllflg Iii-ir p S 5 1.

I lllllllllrlll4 x t I SPARKPLUG CAP The present invention relates to a sparkplug cap, in general, and to a sparkplug cap having a plastic insulating body containing the ignition-wire terminal and the sparkplug terminal, as well as a grounded screening shell which surrounds same, in particular.

The igniting of the fuel-air mixture is effected in gasoline engines today, generally by the customary high-voltage ignition, an igniter being used to produce the ignition spark which jumps over the electrodes (the points) of the sparkplug and ignites the fuel-air mixture. As igniters there are used in this connection magnetos, electronic ignition systems or else the customary battery igniters. As is generally known, a battery ignition system consists of ignition coil, ignition distributor, sparkplugs and ignition switch. The primary current of the ignition coil is taken from the car battery and controlled by the contact breaker by means of the cam. Upon each interruption of the primary current, a highvoltage pulse is produced. The pulses are fed by the spark distributor to the sparkplugs and bring about the sparking. The ignition voltage which must be used for an energy-rich spark is dependent essentially upon the electrode spacing of the sparkplug and the pressure in the combustion space. As a result of the large number of the resistances present in series in the sparkplugs, especially due to, the large resistance caused by the spark distributor, the known ignition systems must be over-dimensioned from the standpoint of voltage without the sparking power being improved. This is due in particular to the fact that there is a phase shift and the voltage leads the ignition current.

In order to bring about a strengthening of the spark, it is known in principle to connect a capacitance, and therefore a condenser, in parallel to the spark gap. In the known devices the condensers are arranged to a greater or lesser extent in the vicinity of the sparkplugs or are formed by capacitively developed ignition cables. These known arrangements and developments of i the condensers in ignition systems have, however, not proven satisfactory or gained a foothold in practice, since the expected increase in power was not obtained, despite the structural expense of the condensers provided for this.

It is one object of the present invention to provide by simple means a condenser as close as possible to the spark gap, which condenser is connected in parallel to the spark gap, by which the sparking power can be increased.

The invention starts out in this connection from a screened sparkplug cap such as is generally customary today in high-power engines. The plastic insulating body which contains the ignition cable terminal and the sparkplug terminal is surrounded in the case of these caps by an electrically conductive screening jacket which is intended to serve for suppressing radio interference. These screened sparkplug caps only poorly and insufficiently satisfy the always stringent conditions concerning radio interference suppression in automobiles.

It is another object of the present invention to provide, proceeding from these known sparkplug caps, a sparkplug cap wherein the ignition cable terminal and/or the sparkplug terminal are formed as a condenser electrode which lies in the plastic insulating body and that, with the utilization of the plastic insulating body as a dielectric, there is formed with the screening jacket a condenser of high capacitance arranged in parallel to the spark gap. The dielectric in this connection has a high electric breakdown strength as well as a high mechanical and thermal dimensional stability.

It is yet another object of the present invention to provide a sparkplug cap in accordance with the previous objectives wherein the screening jacket or the outer condenser electrode is preferably formed either by a metallic sleeve, metallic coil spring, a metallic fabric or an electrically conductive coating, covering or electro-plating, or the like.

It is still another object of the present invention to provide a sparkplug cap in accordance with the previous objectives wherein the condenser connected in parallel to the spark gap in the case of a noise-suppres sion resistance arranged in the plug is connected behind the interference-suppression resistance, as seen in the direction of the ignition current.

The inner condenser electrode which is enclosed by the plastic insulating body is preferably formed as a hollow cylinder or cartridge. In order to obtain a compact unit, the noise-suppression resistance is arranged, in accordance with the present invention, within the hollow cylinder or cartridge and is preferably screened.

The outer condenser electrode, the plastic insulating body and the ignition cable terminal and/or sparkplug cable enclosed thereby form a condenser of a capacity which is variable within the range of the temperature variations and which is influenced by the temperature in the sparkplug.

With these and other objects in view, which will become apparent in the following detailed description, the present invention will be clearly understood in connection with the accompanying drawing, in which:

FIG. Us a schematic circuit diagram showing the arrangement of the condenser;

FIG. 2 is a longitudinal axial section through the sparkplug cap in accordance with the present invention and through the sparkplug inserted in the engine block; and

FIG. 3 is a longitudinal axial section through an angle type cap constituting a second embodiment of the present invention.

Referring now to the drawing, and more particularly to FIG. 1, the ignition current fed by the ignition current lead 10 from the igniter (not shown) is conducted to the center electrode 1, and passes from the latter in the form of a high-voltage arc to the ground electrode 2 of the sparkplug. The resistor R in FIG. 1 is the last of the resistances connected in the circuit in front of the sparkplug electrodes (points) 1, 2 and is formed, for instance, by the breakdown resistance or by the noisesuppression resistor, to be described hereinafter. Behind the resistor R there is connected in parallel to the spark gap 3 and thus in parallel to the center electrode 1 and to the ground electrode 2 a capacitor C of high capacitance which is connected at one end to the ignition current lead 10 and at the other end to the ground 4, operatively.

Let us assume that the voltage which leads the ignition current charges the capacitor C. In this way a phase shift is produced so that voltage and ignition current arrive practically simultaneously in the center electrode 1. Upon the passage of the are from the center electrode 1 to the ground electrode 2 over the spark gap 3 there takes place a capacitive discharge of high current and power. By the ignition current taken from the capacitor C as from storage, the intensity of the spark is increased, as can be noted optically from the fact that the arc becomes wider and brighter at the two electrodes 1, 2 than upon the elimination of the capacitor C. The increase in the intensity of the sparking has a particularly favorable effect on the combustion which takes place free of residues even in case of a poor mixture and strong contamination and leading of the sparkplugs, in particular also in the case that the fuel-air mixture becomes richer, for instance upon the sudden increase in the speed of rotation of the engine and the decrease in the resultant ignition voltage inherent therein.

Referring now again to the drawings, and more particularly to the embodiment of FIG. 2, a sparkplug cap 11 to 19 of the present invention and the sparkplug l to 9 is shown. The sparkplug consists in customary manner of the center electrode 1 extending into the combustion space and a ground electrode 2, a housing 5 connected to the ground 4, an insulator 6, a conductive sealing mass 7, a terminal pin 8 and a coupling nut 9.

Both the elongated cap of the present invention as shown in FIG. 2, and the angle cap shown in FIG. 3, are conductively connected by a connecting spine 11 with the ignition current cable 10. The two sparkplug caps comprise essentially a tubular plastic insulating body 12 (body 12' in FIG. 3), the upper opening of which forms a cable holder for the ignition current cable and receives at this end the conductive ignition cable terminal 14 and on the end facing away therefrom the conductive sparkplug terminal 13. The plastic insulating body 12 is in its turn surrounded by a conductive screening shell 16 which in this embodiment is formed by two half shells of sheet metal closely surrounding the plastic insulating body 12, the half shells being held together at the lower end by a spring ring 16a and resting together against ground 4 or housing 5 of the sparkplug.

In order to form a capacitor of high capacitance, the ignition cable terminal 14 and/or the sparkplug terminal 13 is widened in accordance with the invention to form one condenser electrode, while the other condenser electrode is formed by the conductive screening shell 16 which is connected to ground 4. Depending on the capacitance of the capacitor C, the plastic insulating body 12 separating the two condenser electrodes and I6 is formed as a dielectric of high dielectric strength and of mechanical and thermal dimensional stability.

Insulating materials having such properties are already known and are used in electrical engineering. These insulating materials which generally have a base of phenol cresol together with fillers, such as sawdust, or the like, have a tendency merely to absorb water, which has a detrimental effect on the dielectric strength. The water absorption can be eliminated, however, by a special treatment of this insulating material.

In order to eliminate radio interference on the part of the sparkplug cap, a noise-suppression resistor R is provided therein in accordance with the invention. In order to obtain a compact construction, this noise-sup pression resistor R is contained within the inner capacitor electrode 15 which is formed as a hollow cylinder or as a cartridge. The noise-suppression resistor R lies, in this connection, with the interposition of a conductive spring 17, which also takes up expansions in length, against the ignition cable terminal 14 and at the lower end against the bottom of the cartridge. The ignition cable terminal [4 is in this connection held spaced by an insulating liner 18 from the inner capacitor electrode 15, so that in this way the circuit shown in FIG. I is assured. The noise-suppression resistor R is supported otherwise in screened fashion in the capacitor electrode 15.

The cartridge consisting of the connecting spline 11, the sparkplug terminal 13, the conductive ignition cable terminal 14, the inner capacitor electrode 15, the spring 17, the insulating liner 18 and the noise-suppression resistor R is inserted as a structural unit from the end of the sparkplug mount into the tubular plastic insulating body 12 and preferably fastened on both ends by a sealing composition 19 introduced therein.

The angular cap shown in FIG. 3 is developed in accordance with the same principle of the present invention. The primed reference characters refer to the corresponding elements of FIG. 2. The sparkplug 1 to 9 of FIG. 2, however, is not shown in FIG. 3 for clarity of illustration. Due to the angular shape, it is merely necessary for the sparkplug terminal 13 to be introduced from the one side, and the one capacitor electrode 15 which is formed as the cartridge or hollow cylinder must be inserted into the plastic insulating body 12 from the other side. The electrical connection between these two parts is obtained also by a spring 17" at the point of bend, which spring, as an elastic connection, takes up the thermal expansions of the individual parts better than a rigid connection. A second conductive spring 17' electrically connects one end of the noisesuppression resistor R to conductive ignition cable terminal 14 and via the connecting spline 11' to the ignition current cable (not shown in FIG. 3) in the cable holder opening. An insulating line 18' spaces the ignition cable terminal 14' from the inner capacitor electrode 15'. The outer capacitor electrode 16' conforms to the angular shape of the cap partly surrounding the insulating body 12'. A sealing composition 19' seals the sparkplug terminal 13' to the insulating body 12'.

In several modified embodiments (not shown) the screening shell which forms the outer capacitor electrode I6 is formed by a tightly turned coil spring or a metallic fabric. In another embodiment (not shown) the screening shell is formed by an electrically conductive coating, application or an electroplating. This manner of development of the outer capacitor electrode is particularly favorable from the standpoint of manufacturing technique, since in this way expensive embossings of sheet metal can be eliminated. In all embodiments, however, assurance must be had that the conductive screening shell rests conductively against the ground part of the sparkplug seat.

By the ingenious arrangement and shaping of the metal parts of the cap, the capacitor C is arranged very close to the spark gap 3. This has the advantage that the sparkplug becomes noncritical with respect to the influence of moisture, since the high voltages are con verted into high currents at the sparkplug terminal 13. Another advantage of this arrangement is that the sparkplug transfers to the capacitor C the heat variations occurring in the combustion chamber, due to different motor output in the manner of a measurement detector. This has the result that the capacitor C changes its storage capacitance corresponding to the changing operating conditions in the combustion chamber. As extensive test measurements have shown, the capacitor electrode embedded in the insulating material expands upon heating and thus not only increases its surface but at the same time also exerts a pressure on the dielectric 12 enclosed between the outer capacitor electrode 16 and the inner capacitor electrode 15, which leads to an increase in the storage capacitance. In this way a decrease in compression which occurs upon an increase in the temperature of the engine is automatically counteracted. The decrease in compression is therefore intercepted by a higher discharge power and the higher sparking energy resulting therefrom. The adjustment is effected automatically. In order that one obtains at the same time a faster impingement of the molecules, the flame front in the cylinder is widened, it is subject to a different time constant, and the condensation zone moves back. The heat exchange in the cylinder is improved by a decreased depositing of carbon or the absence thereof. By the more intensive ignition, one can use mixtures which are leaner but are more ready to ignite. However, in all cases there is a self-cleaning effect of the sparkplugs.

In the entire ignition system, the capacitance of the sparkplug cap of the invention which is connected parallel to the spark gap has the following effect. Heretofore, the burning at the interrupter contact was punctiform (anode-cathode). The voltage in the secondary circuit is not fully broken down (magnetic field), since the time constant is too short. The built-in capacitance C sees to it that the excess voltage is taken from the circuit and converted into current. Upon the next ignition, the stored residual electromagnetic force is practically removed completely. Instead of the customary punctiform erosion, there now takes place a surface erosion. In this way the life of the interrupter contact is increased and the ignition adjustment remains correct for a longer period of time.

Furthermore, the capacitance of the capacitor C is dimensioned as a function of the power of the source of current supplying the ignition current, and the electrode spacing between the center electrode 1 and the ground electrode 2 of the sparkplug 1 to 9.

Herein plastic means any artificial, synthetic or plastic material.

While I have disclosed several embodiments of the present invention, it is to be understood that these embodiments are given by example only and not in a limiting sense.

Iclaim:

l. A sparkplug cap, comprising a grounded outer metallic sleeve,

an inner metallic member being operatively connectable with an ignition cable,

a sparkplug having a spark plug gap,

a dielectric member separating said inner metallic member and said outer metallic sleeve,

said inner metallic member and said outer metallic sleeve with said dielectric member being formed as a capacitor,

said capacitor being disposed in parallel to said ignition spark gap, and

a noise-suppression resistor operatively electrically connected in series to the parallel combination of said capacitor and said spark gap and arranged before said capacitor with relation to the direction of the ignition current to said spark plug gap.

2. The sparkplug cap, as set forth in claim I, wherein said sleeve is a coil spring.

3. The sparkplug cap, as set forth in claim I, wherein said sleeve is a metallic fabric.

4. The sparkplug cap, as set forth in claim 1, wherein said sleeve forms an electrically conductive application or coating.

5. The sparkplug cap, as set forth in claim 1, wherein said sleeve is electroplated.

6. A sparkplug cap for sparkplugs having a central electrode and a grounded electrode spaced therefrom forming a spark plug gap, comprising an ignition cable terminal adapted to be connected to an ignition cable,

a sparkplug terminal operatively electrically connected to said ignition cable terminal,

a plastic insulating body containing said ignition cable terminal and said sparkplug terminal,

said sparkplug terminal connectable operatively electrically to said central electrode,

a grounded screening shell at least partly surrounding said insulating body,

at least one of said terminals being formed to constitute a first capacitor electrode within said insulating body,

said screening shell constituting another capacitor electrode,

said insulating body constituting a dielectric,

said capacitor electrodes and said dielectric forming cooperatively a capacitor of high capacitance connected in parallel to said spark plug gap,

a noise-suppression resistor operatively electrically connected in series to the parallel combination of said capacitor and said spark gap and arranged before said capacitor with relation to the direction of the ignition current to said spark plug gap,

said first capacitor electrode is formed as a hollow cartridge, and

said noise-suppression resistor is arranged within said hollow cartridge.

7. The sparkplug cap, as set forth in claim 6, wherein said noise-suppression resistor is arranged screened in said hollow cartridge.

8. The sparkplug cap, as set forth in claim 1, wherein said metallic member is enclosed in said dielectric member and is formed as a hollow cartridge.

9. The sparkplug cap, as set forth in claim 8, wherein said cartridge is a hollow cylinder.

10. The sparkplug cap, as set forth in claim 1 wherein said capacitor is influenced by the temperature at said sparkplug and having variable capacitance within the range of the temperature variations.

11. The sparkplug cap, as set forth in claim 1,

wherein said inner metallic member is formed as a hollow cartridge, and

said noise-suppression resistor is arranged within said hollow cartridge. 

1. A sparkplug cap, comprising a grounded outer metallic sleeve, an inner metallic member being operatively connectable with an ignition cable, a sparkplug having a spark plug gap, a dielectric member separating said inner metallic member and said outer metallic sleeve, said inner metallic member and said outer metallic sleeve with said dielectric member being formed as a capacitor, said capacitor being disposed in parallel to said ignition spark gap, and a noise-suppression resistor operatively electrically connected in series to the parallel combination of said capacitor and said spark gap and arranged before said capacitor with relation to the direction of the ignition current to said spark plug gap.
 2. The sparkplug cap, as set forth in claim 1, wherein said sleeve is a coil spring.
 3. The sparkplug cap, as set forth in claim 1, wherein said sleeve is a metallic fabric.
 4. The sparkplug cap, as set forth in claim 1, wherein said sleeve forms an electrically conductive application or coating.
 5. The sparkplug cap, as set forth in claim 1, wherein said sleeve is electroplated.
 6. A sparkplug cap for sparkplugs having a central electrode and a grounded electrode spaced therefrom forming a spark plug gap, comprising an ignition cable terminal adapted to be connected to an ignition cable, a sparkplug terminal operatively electrically connected to said ignition cable terminal, a plastic insulating body containing said ignition cable terminal and said sparkplug terminal, said sparkplug terminal connectable operatively electrically to said central electrode, a grounded screening shell at least partly surrounding said insulating body, at least one of said terminals being formed to constitute a first capacitor electrode within said insulating body, said screening shell constituting another capacitor electrode, said insulating body constituting a dielectric, said capacitor electrodes and said dielectric forming cooperatively a capacitor of high capacitance connected in parallel to said spark plug gap, a noise-suppression resistor operatively electrically connected In series to the parallel combination of said capacitor and said spark gap and arranged before said capacitor with relation to the direction of the ignition current to said spark plug gap, said first capacitor electrode is formed as a hollow cartridge, and said noise-suppression resistor is arranged within said hollow cartridge.
 7. The sparkplug cap, as set forth in claim 6, wherein said noise-suppression resistor is arranged screened in said hollow cartridge.
 8. The sparkplug cap, as set forth in claim 1, wherein said metallic member is enclosed in said dielectric member and is formed as a hollow cartridge.
 9. The sparkplug cap, as set forth in claim 8, wherein said cartridge is a hollow cylinder.
 10. The sparkplug cap, as set forth in claim 1 wherein said capacitor is influenced by the temperature at said sparkplug and having variable capacitance within the range of the temperature variations.
 11. The sparkplug cap, as set forth in claim 1, wherein said inner metallic member is formed as a hollow cartridge, and said noise-suppression resistor is arranged within said hollow cartridge. 